A vigorous angiogenic response is a prominent component of normal wound repair. Within healing wounds, angiogenesis proceeds until vessel density more than doubles compared to uninjured tissue;most of these new vessels subsequently undergo apoptosis and are removed. While the mechanisms that guide the pro- angiogenic phase of healing are well-understood, the factors that regulate vascular regression in wounds are not yet clear. This project proposes to examine the mechanisms of vascular regression in the wound using well-established in vivo models. The overarching goal of this research is to evaluate the important molecular and spatio-temporal factors that cause blood vessel pruning and blood flow stabilization, and thereby contribute to successful wound resolution. The central hypothesis is that specific endogenous anti-angiogenic factors, including pigment epithelium-derived factor (PEDF) and vasostatin-I, drive vascular regression, allowing the resolving wound to come to vascular homeostasis. The primary aim of the current project is to discover the role of PEDF and vasostatin-I in the context of wound healing. The project will explore the mRNA and protein expression patterns of PEDF and vasostatin-I throughout the time course of healing in a well- characterized murine model of full-thickness dermal wounds. These proteins will be localized in the wound to evaluate the local cellular and structural environment with which they associate and interact. Comprehensive proof-of-function in vivo experiments will be performed to assess the role of endogenous PEDF and vasostatin- I in the resolving wound. These experiments will include the addition of supra-physiological levels of exogenous anti-angiogenic recombinant proteins to healing wounds. Also, interference with function of endogenous mediators will be performed via a novel method of delivery of small interfering RNA (si-RNA) nanoparticles and/or antibodies, followed by an assessment of their effect on wound vascularity using non- invasive laser Doppler imagining. The long term goal of this project is to develop a comprehensive understanding of the complex mechanisms that regulate wound angiogenesis. This knowledge will assist in the development of novel therapeutics to modify dysfunctional neovascularization and/or vascular regression in many human pathological conditions like cancer and arthritis, and will be especially applicable to the treatment of poorly healing wounds. Public Health Relevance: Dysfunctional blood vessel growth or regression is a hallmark of many human pathological conditions including cancer, arthritis, and diabetes-induced delayed wound healing. This study aims to evaluate the potential role of two mediators of blood vessel regression, PEDF and vasostatin-I, to further our understanding of the important regulatory mechanisms that contribute to successful wound resolution. This understanding will bring us closer to the development of more effective treatment methods for patients suffering from these diseases.